Results of international achievement surveys such as the Programme in International Student Assessment have consistently reported an achievement gap between immigrant and non-immigrant student populations around the world. This paper unpacks this persistent achievement gap by examining key characteristics that influence the performance of first- and second-generation immigrant students as well as the policies and practices that are associated with enhanced educational outcomes. A multi-layered framework is proposed to help policymakers juxtapose key characteristics of their immigrant students' achievement against individual, family, school, community, and host society characteristics and policies. The discussion also underscores the importance of connecting this multi-layered framework with other important sectors within governments such as those responsible for the economy, health, social protection, and immigration. This paper also examines limitations with current large-scale data sets and the implications for research and policy analysis.